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10-05-2009, 09:15 AM   #1
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K20D autofocus calibration

All,

After testing the AF on my Pentax 17-70mm and realising I needed to tweak the AF to +4, I decided to calibrate my Sigma 100-300mm f/4 this afternoon too. I had taken shots of swans earlier in the day and noticed that they weren't as perfectly focussed as they should be.

I took a serious of tripod mounted shots from AF adjusment +0, +2, +4, +6, +8 and +10. There was quite a difference between +0 and +4 in terms of focus / sharpness, so it's clear that both my 17-70mm and 100-300mm need to have +4 on the AF adjustment front.

I have two questions:

1) It seems two seperate lenses from seperate manufacturers need the same level of adjustment, that suggests that my body is slightly out. Is +4 a front-focus or back-focus issue?

2) Does the K-7 have this AF adjustment in body, or only by way of a debug menu?

Thanks

10-05-2009, 03:18 PM   #2
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QuoteOriginally posted by Big G Quote
1) It seems two seperate lenses from seperate manufacturers need the same level of adjustment, that suggests that my body is slightly out. Is +4 a front-focus or back-focus issue?
Seems likely that the body is slightly out.
With positive values you are correcting back focus. But you should see that from your test images.
You may want to look at these AF adjustment hints.

QuoteOriginally posted by Big G Quote
2) Does the K-7 have this AF adjustment in body, or only by way of a debug menu?
The K-7 supports AF adjustment for several lenses without resorting to a debug menu.
10-06-2009, 04:53 AM   #3
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Great, thanks a lot .
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